Determination of ammonia, creatinine and inorganic cations in urine using CE with contactless conductivity detection

CE with capacitively coupled contactless conductivity detection (CID) was used to determine waste products of the nitrogen metabolism (ammonia and creatinine) and of biogenic inorganic cations in samples of human urine. The CE separation was performed in two BGEs, consisting of 2 M acetic acid + 1.5 mM crown ether 18-crown-6 (BGE I) and 2 M acetic acid + 2% w/v PEG (BGE 11). Only BGE 11 permitted complete separation of all the analytes in a model sample and in real urine samples. The LOD values for the optimized procedure ranged from 0.8 mu M for Ca2+ and Mg2+ to 2.9 mu M for NH4+ (in terms of mass concentration units, from 7 mu g/L, for Li+ to 102 mu g/L, for creatinine). These values are adequate for determination of NH4+, creatinine, Na+, K+, Ca2+ and Mg2+ in real urine samples.